Toxic Substances Hydrology Program
Microorganisms Degrade MTBE Even at Winter Ground-Water Temperatures
Shallow ground waters in northern climates often have temperatures below 10° Celsius (C) [50° Fahrenheit (F)] during the winter season. The ability of microorganisms to degrade contaminants under these conditions has long been questioned by the scientific community because microbial activity often decreases with decreasing temperatures and because rates of biodegradation typically are assumed to be low or insignificant at ground-water temperatures of 5°C (41°F) or less. The effects of seasonal, cold ground-water temperatures on the biodegradation of methyl tert-butyl ether (MTBE) in the subsurface are a particular concern because MTBE contamination is widely reported in shallow ground water with seasonal temperatures at or below 5°C (41°F).
U.S. Geological Survey (USGS) scientists recently investigated the effects of seasonal cold ground-water temperatures on microbial MTBE degradation in sediments from two sites (Ronan, Montana, and Almena, Kansas) having MTBE contamination and mean ground-water temperatures of 10°C (50°F). The scientists found that the microbial communities in both sediments were able to biodegrade MTBE to carbon dioxide (CO2) at temperatures as cold as 4°C (39.2°F). These results indicate that microbial degradation can continue to contribute to the natural attenuation of MTBE in ground water even during winter cold-temperature conditions. This continued degradation is particularly important because winter-time use of fuel oxygenates, among which MTBE is currently (2006) the most common, is mandatory in many urban areas in the United States to abate air pollution from cars. Federal and state regulators and environmental cleanup professionals can use the results of this study to make informed decisions concerning the remediation of MTBE contamination at leaking underground gasoline storage tanks in northern climates.